This invention relates to the manufacture of integrated masses of shaped particulate material such as foundry cores, and the like, by hardening gas catalyst-hardenable resin-bound shaped particulate masses, such as for example a sand mass with a gas catalyst.
The use of polymerizable liquid binders for the purpose of hardening binder-coated sand masses such as foundry sand mixes, for example, is well known. Heretofore, two general types of applications have been widely considered and adopted, namely those procedures in which the catalyst is admixed with the resin binder prior to the shaping of the catalyzed sand mass, and those procedures in which the binder is initially applied, and the catalyst is subsequently contacted therewith after the sand mass is shaped.
The procedures which involved catalyzing prior to shaping inherently suffered several serious short-comings. For example, with respect to the "cold cure" systems, the polymerizable binder, immediately upon admixing of catalyst therewith, tended to advance with resulting increase in viscosity. It is widely appreciated that the strength of the resulting hardened articles such as foundry sand articles, diminished as the binder inadvertently advanced in viscosity prior to the placement and packing of the curing sand mix in the sand shaping element. To overcome this short-coming, it was also widely appreciated that relatively slower acting catalyst could be employed, and that the catalyzed binder sand mixture could be heated after the sand mass had been shaped within the shaping element. These so-called "hot box" methods involved much higher capital investments; and the need for more complicated and more expensive shaping elements has been regarded as a definite short-coming of these "hot box" methods.
As an alternative to pre-mixing the catalyst and binder prior to the placement of the hardenable sand mix in a shaping element, it has been suggested to pack uncatalyzed binder coated sand in shaping elements, and subsequently contact the binder coating with gaseous catalyst. The packed binder-coated sand is extremely permeable with respect to the passage of gas therethrough.
The use of gas catalyst is well known in connection with the polymerization of gas catalyst polymerizable binder to produce shaped articles such as foundry sand cores and molds. Several processes have been suggested heretofore including the passing of a gaseous catalyst through shaped sand masses in which the sand particles have been precoated with a liquid gas-catalyst-polymerizable binder. In addition, it has been disclosed heretofore to use a procedure wherein the shaped sand mass is subjected to a vacuum, and in which the gas catalyst is released into the "vacuumized" sand mass for cure.
As a practical matter, however, these processes have also been generally less than satisfactory in the manufacture of shaped sand articles such as, for example, foundry articles. For example, the passing of gas catalyst through a complex shaped sand mass under pressure has been regarded undesirable inasmuch as remote portions of complex sand articles sometime remained uncured due to undesirable channeling of the gas catalyst through other regions of the shaped sand mass, none reaching the unhardened remote region.
In addition, the vacuum methods heretofore suggested have not proved completely satisfactory for foundry use for several reasons. First of all, the degree to which a vacuum can be induced in a foundry is, generally speaking, far less than the extent necessary to produce a "perfect vacuum". The vacuum methods suggested heretofore have proven to be unsatisfactory when the partial vacuums which are conveniently induced in a foundry environment are induced, e.g. above 50 mm Hg, or even above 300 mm Hg, with the result that some crucial portions of the shaped sand mass destined to confine molten metal remain uncured after catalyst gassing. These uncured portions generally separate and fall under force of gravity from the cured portion of the sand mass, upon stripping. Also, some gassing methods and apparatus heretofore suggested have generally involved the forming of an article in a core box, and possibly removing the shaped article from the core box, and placement of the shaped article which is sustained in shape only by its green strength, for example, in a gassing chamber for subsequent hardening by a gas catalyst. The placement of the article in a gassing-chamber and even the placement of a core box in a gassing chamber, has been less than desirable inasmuch as copious quantities of gas catalyst are required and vast excesses of the gas catalyst are lost due to the relatively large void in the vacuum chambers. The volume of the gassing chamber is usually relatively large with respect to the volume of the interstices of the shaped sand mass. The portion of the gas catalyst occupying the void space of the gassing chamber after the article is gassed is, of course, ineffective and is unused in the actual polymerization of the gas curable binder, and is, in that sense, totally wasted. In addition, such inefficient use of gaseous catalyst has encountered increasing objection in recent years due to increased awareness of environmental pollution by the excess wasted gas catalyst.